Catalyst systems for polycondensation reactions

ABSTRACT

The invention concerns new catalyst systems for the synthesis of polyesters, for instance for the manufacture of polyethylene terephthalate and its copolyesters. The catalyst system according to the invention consists of an antimony or germanium compound, a heterogeneous catalyst component and an ester of phosphoric acid or of phosphorous acid as stabilizer. The polycondensation rate both in the liquid phase and in solid phase polycondensation (solid state) can be increased by 30-100 percent with the smallest additions of the heterogeneous component.

The invention concerns new catalyst systems for the synthesis ofpolyesters, for instance the manufacture of polyethylene terephthalateand its copolyesters.

The synthesis of polyesters such as polyethylene terephthalate requiresthe use of catalysts in the polycondensation steps (melt phase andpossibly solid state). A number of patents can be found in theliterature that describe the use of catalytically active substances.Today, antimony and titanium compounds are used in particular inindustry, in the manufacture of polyethylene terephthalate. This is alsoreflected in the numerous patents that describe the use of suchcompounds. Polyester-soluble antimony compounds are described aspolycondensation catalysts in U.S. Pat. Nos. 3,965,071, 3,998,793,4,039,515, 4,116,942, 4,133,800, 4,454,312, 5,750,635 and 5,780,575.Modified antimony derivatives (stabilized by substances with doublebonds to prevent reduction to metallic antimony) are for instance thesubject of patents U.S. Pat. No. 4,067,856, U.S. Pat. No. 4,067,857 andU.S. Pat. No. 4,130,552. Antimony salts of trimellithic acid esters arealso used as catalysts in the manufacture of polyethylene terephthalate(U.S. Pat. No. 5,478,796).

A combination of sulfonic acid, titanate and antimony (or germanium)compounds is the object of U.S. Pat. No. 5,905,136. U.S. Pat. Nos.5,286,836 and 5,714,570 mention combinations of antimony and titaniumcompounds as catalytically active. U.S. Pat. No. 6,372,879 must also bementioned in this context. The synergistic effects of catalyst systemsdescribed in this patent appear when complex titanium/antimony/(oxalate)systems are used. Germanium compounds have also been described ascatalysts for the polycondensation reaction (U.S. Pat. No. 5,378,796,U.S. Pat. No. 5,830,981, U.S. Pat. No. 5,837,786 and U.S. Pat. No.5,837,800). However, for economic reasons the use of these compounds hasnot become widespread.

The combination of several metal compounds is described in U.S. Pat. No.4,122,107 (Sb/Zn(Ca,Mn); U.S. Pat. No. 4,356,299, U.S. Pat. No.4,501,878 and U.S. Pat. No. 5,286,836 (Ti/Sb); U.S. Pat. No. 5,565,545and U.S. Pat. No. 5,644,019 (Sb/Ge); U.S. Pat. No. 5,608,032 and U.S.Pat. No. 5,623,047 (Sb/Co(Mg,Zn,Mn,Pb). At least one component of thesecomplex catalysts is a classic” polycondensation catalyst, eitherantimony, titanium or germanium. In the most favorable case, theactivity of these systems lies in the range of activity of a pureantimony compound.

Finely dispersed titanates are the object of U.S. Pat. No. 5,656,716.

Jointly precipitated titanium and silicon compounds and titanium andzirconium compounds are described in U.S. Pat. Nos. 5,684,116 and5,789,528.

A polycondensation catalyst based on zeolites (alkali or alkalineearth-modified alumino-silicate) is protected by U.S. Pat. No.5,733,969.

The object of patent WO 01/42335 is the use of hydrotalcites aseffective catalysts for polycondensation reactions. These compoundsexhibit a higher activity than for instance antimony compounds,particularly in the liquid phase (melt phase).

The use of antimony compounds is especially preferred, since theselectivity of the catalyzed polycondensation reactions is highest andthe reaction rate of the polycondensation is adequate. The content inundesirable degradation products, such as acetaldehyde, is lowest in theprocessed polyester, compared to titanium compounds, for instance.

However, the use of antimony compounds such as antimony oxide, antimonyacetate or antimony glycolate as catalysts for polycondensationreactions is permissible only within defined limits, since thesesubstances are physiologically objectionable, as heavy metal compounds.For this reason it is not possible to increase the reaction rate of thepolycondensation reactions indefinitely by increasing the catalystconcentration. Another cause for the economically unsatisfactoryreaction rate is the fact that the rate of the two reaction steps (meltphase and solid state) depends not only the temperature, but also verystrongly on the diffusion of volatile reaction products, such asethylene glycol.

The invention is based on the task of developing a catalyst system forthe synthesis of polyesters, in particular poly(ethylene terephthalate)and its copolyesters that at clearly increased catalytic activity, doesnot affect or affects only minimally the application-related propertiesof the polyester. In addition, the use of these systems should bephysiologically safe.

It was very surprisingly found that using a combination of certain inpart already known polycondensation catalysts, the reaction rates in themelt phase and in the solid state during the manufacture of polyethyleneterephthalate could be clearly increased, without negatively affectingthe quality of the polyester. These new catalyst systems according tothe invention consist of:

-   a) a classic polycondensation catalyst of antimony, germanium or    titanium compounds such as antimony acetate, antimony oxide,    antimony glycolate, germanium oxide or tetrabutyl titanate,-   b) a second, heterogeneous catalyst such as hydrotalcite or    hydrotalcite-like compounds of general formula    [M(II)_(1-x)M(III)_(x)(OH)₂]^(x+)(A^(n−) _(x/n)).mH₂O    -   in which M(II) stands for divalent metals, in particular        magnesium, zinc, nickel, copper,    -   iron(II) or cobalt(II); M(III) for trivalent metals, such as        aluminum or iron(III) and    -   A for anions such as carbonates, borates or titanyl compounds,        and-   c) a stabilizer, preferably an ester of phosphoric acid or    phosphorous or phosphonic acid.

It was surprisingly found that combinations of these catalysts exhibitsynergistic effects. The polycondensation rate in the liquid phase attemperatures of 250-300° C. can be increased by 30->10 percent with thesmallest additions of the heterogeneous component (approx. 5-50 ppm).The situation is similar in solid phase polycondensation (solid state)at temperatures of 180-230° C. For additions of 5-50 ppm of theheterogeneous component, only little catalytically active in the solidstate, here too the reaction rate of this polycondensation reaction canbe increased by up to 50 percent

These new catalyst systems are preferably used with the followingcomposition:

-   antimony or germanium compounds 50-1000 ppm, heterogeneous catalyst    1-100 ppm (depending on particle size) and esters of phosphoric or    phosphorous acids, 5-500 ppm. The heterogeneous catalysts are    preferably used with particle sizes between 50 nm and approx. 3 μm.    Systems with a ratio of homogeneous/heterogeneous-acting catalyst of    from 100:1 to 1:5, preferably of 80:1 to 5:1, are especially    preferred.

The invention will be elucidated below by means of implementationexamples. The intrinsic viscosity (IV) of the synthesized polyesters wasdetermined on an instrument of the Schott company (AVSPro), on 250 mgpolyester dissolved in 50 ml phenol/dichlorobenzene (1:1).

The acetaldehyde determination in the extruded products used thefollowing procedure:

-   The PET material was precooled in liquid nitrogen and milled in an    ultracentrigal mi. The comminuted material was immediately weighed    into a headspace vial and sealed gas-tight with a septum. After 90    min of thermostatting at 150° C. in the headspace sampler, an    aliquot of gas at a known pressure was injected onto the GC column.

The following procedure was used to synthesize the polyesters:

-   In a 200L-alloyed steel reactor were preplaced a suspension of    60.675 kg terephthalic and 1.44 kg isophthalic acid in 31.6 kg    ethylene glycol. While stirring, add to this reaction mixture the    appropriate amount of antimony triacetate, 8.125 g cobalt acetate    tetrahydrate in 1000 g ethylene glycol and 34.65 g    tetramethylammonium hydroxide in 500 g ethylene glycol. The sealed    reactor was heated to 272° C. The slow depressurization of the    pressurized container began at 2.8 bar. After approx. 20 min, the    heterogeneous catalyst in 500 g ethylene glycol and 4 g Irgafos    P-EPQ as glycolic solution were added, at normal pressure.

Liquid phase polymerization was next started, by slowly applying avacuum. After approx. 60 min the final vacuum of approx. 4 mbar wasattained. The end of the reaction was indicated by achieving a definedtorque.

The reaction vessel was depressurized with nitrogen and the reactor wasemptied into a water bath through various nozzles, over a period ofapprox. 60 minutes. The product strands were granulated immediately.

Table 1 shows an overview of the reaction times of the liquid phasepolycondensation. TABLE 1 Reaction time and viscosity in liquid phasepolycondensation as a function of the catalyst system used heterogeneousReaction Viscosity number intrinsic Catalyst catalyst time per DIN ISOviscosity Experiment No. (ppm) (ppm) (min) 1628/5 (ml/g) (dl/g)³⁾ 1(Comparison example) Antimony acetate (640)¹⁾ 0 185  74.2 0.643 2(Implementation example) Antimony acetate (640)¹⁾ Hydrotalcite Pural Mg61 HT⁴⁾ (50) 90 78.9 0.68 3 (Implementation examplel) Antimony acetate(640)¹⁾ Hydrotalcite Pural Mg 61 HT (25) 93 77.9 0.672 4 (Implementationexample) Antimony acetate (640)¹⁾ Hydrotalcite Pural Mg 61 HT (10) 9575.4 0.661 5 (Implementation example) Antimony acetate (490)²⁾Hydrotalcite Pural Mg 61 HT (50) 90 80.2 0.69¹⁾corresponds to a concentration of approx. 260 ppm antimony in thepolyester²⁾corresponds to a concentration of approx. 200 ppm antimony in thepolyester³⁾in o-chlorophenol⁴⁾Trade name of the SASOL companyTable 1 clearly shows that even the smallest additions of theheterogeneous component are able to markedly increase thepolycondensation rate in the melt phase.

If the polyester is to be used to package foods, then thepolycondensation reaction in liquid phase is followed by a so-calledsolid-state polycondensation. The purpose of this procedural step is todrastically reduce the byproducts formed during the melt phasepolycondensation—such as acetaldehyde—and simultaneously increase theintrinsic viscosity. The viscosity increase is necessary to achieve thedesired mechanical properties in the end product. This reaction isperformed at temperatures of 180-230° C. The procedural step isespecially cost-intensive because of the need to use pure nitrogen asprocess gas.

The solid-state polycondensation occurs according to the proceduredescribed below. The solid-state reaction was performed in a laboratoryglass reactor of the BÜHLER Co., in a pulsating fluidized bed. 3 kgamorphous PET pellets were placed in the reactor preheated to 150° C.The volume flow of the process gas (nitrogen) flowing through the PETwas of 125 Nm³/h. Approx. 15 m³/h nitrogen were removed from thecirculation through a removal loop and replaced with network nitrogen.The crystallization and drying of the PET was performed at 170° C. overa period of 2.5 h following the addition of the amorphous PET pellets.The solid-state reaction occurred next over a period of 6 h, at atemperature of 210° C. and at the parameters mentioned (volume flow,amount removed). 50 g samples were taken at regular intervals andwithout affecting the process parameters.

Table 2 below shows the values of intrinsic viscosity obtained duringthe solid state polycondensation of polyesters with various catalystsystems. TABLE 2 SSP rate as a function of the catalyst system CatalystSSP time ΔIV Experiment No. system (h) (dl/g) 1 (Comparison example) 260ppm Sb 0 0 2 0.058 4 0.116 7 0.173 2 (Implementation example) 200 ppm 00 Sb/50 ppm HT/ 1.75 0.061 100 ppm P-EPQ 3 0.112 4.75 0.163 6 0.202 3(Implementation example) 260 ppm 0 0 Sb/25 ppm HT/ 1.75 0.079 150 ppmP-EPQ 3 0.125 4.75 0.166 6 0.204 4 (Implementation example 260 ppm 0 0Sb/50 ppm HT/ 1.75 0.068 100 ppm P-EPQ 3 0.115 4.75 0.18 6 0.215Table 2 illustrates the significant effect of the catalyst systemaccording to the invention on the reaction rate in solid-statepolycondensation.

1. Catalyst systems for the synthesis of polyesters, for instance forthe manufacture of polyethylene terephthalate and its copolyesters,consisting of a) an antimony, germanium or titanium compound b) aheterogeneous catalyst and c) optionally a stabilizer.
 2. Catalystsystems for polycondensation reactions according to claim 1,characterized by the antimony or germanium compound used being antimonyacetate, antimony oxide, antimony glycolate, germanium oxide ortetrabutyl titanate.
 3. Catalyst systems for polycondensation reactionsaccording to claim 1, characterized by the heterogeneous catalyst usedbeing hydrotalcites of general formula[M(II)_(1-x)M(III)_(x)(OH)2]^(x+(A) ^(n−) _(x/n)).mH₂O, in which M(II)are divalent metals, in particular magnesium, zinc, nickel, copper,iron(III) or cobalt(II); M(III) are trivalent metals, for instancealuminum or iron(III) and A are anions, for instance carbonate, borateor titanyl compounds.
 4. Catalyst systems for polycondensation reactionsaccording to claim 1, characterized by the stabilizers used being estersof phosphoric acid or of phosphorous or phosphonic acids.
 5. Catalystsystems for polycondensation reactions according to claim 1,characterized by using 50-1000 ppm antimony or germanium compound, 1-100ppm heterogeneous catalyst and 5-500 ppm stabilizer.
 6. Catalyst systemsfor polycondensation reactions according to claim 1, characterized bythe heterogeneous catalyst fraction having a particle size of 50-100 nm.7. Catalyst systems for polycondensation reactions according to claim 1,characterized by the ratio of homogeneous to heterogeneous catalystfractions being of 100:1 to 1:5.
 8. Catalyst systems forpolycondensation reactions according to claim 7, characterized by theratio of homogeneous to heterogeneous catalyst fractions being of 80:1to 5:1.
 9. Utilization of polyethylene terephthalate produced accordingto the claims above for the manufacture of bottles, sheets and fibers.